#include <iostream>
using namespace std;
//求d的开三次方根
int main()
{
    double d;
    scanf("%lf",&d);
    double l = 0 , r = d;
    while(r-l >= 1e-8)
    {
        double mid = (l + r)/2;
        if(mid*mid*mid <= d) l = mid;
        else r = mid;
    }
    printf("%lf",l);
    return 0;
}